Actuator including mechanism for converting rotary motion to linear motion

ABSTRACT

An active vibration control device is provided that is configured to control the position of a body relative to a reference frame. The control device includes sensors that provide input signals corresponding to movement of the body in at least one direction, a rotary rotary actuator configured to control the position of the body, and four-bar linkage connecting the rotary rotary actuator to the body. The linkage converts the rotary motion output from the rotary actuator into a linear motion of the body. The controller, based on the input signals from the reference frame sensors, provides control signals to the rotary rotary actuator which acts through the linkage to position the body in the at least one direction relative to the position of the reference frame.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 12/732,321, published as U.S. Published Pat. App.2011-0233364-A1, entitled “Actuator Including Mechanism for ConvertingRotary Motion to Linear Motion”, filed Mar. 26, 2010 by Breen et al.,which is herein incorporated by reference in its entirety.

BACKGROUND

Active vibration control systems have been employed to control vehicleseat vibration. For example, as a replacement for passive systemsincluding springs and dampers which reduce seat response to vehiclevibration, active vibration control systems detect seat vibration andcontrol the position of the seat to cancel detected motion and therebyisolate the seat from vehicle vibration. Such active vibration controlsystems may include a linear actuator controlled by a controller. Thelinear actuator is positioned below the seat to control seat positionrelative to the vehicle frame. For example, the linear actuator mayinclude a linear electromagnetic motor, including an armature fixed atone end to the seat. The armature linearly extends and retracts relativeto a stator based on control signals from the controller, therebypositioning the seat.

Controlled linear actuators have application to systems other thanvehicle seat vibration control. For example, controlled linear actuatorsare also known to be used in vehicle wheel suspension systems and inengine valve control systems.

In many applications, a challenge associated with using such linearactuators to control object position includes providing a linear motorproviding sufficient linear travel within a limited space, for examplebetween the seat and the floor in an active seat vibration controlsystem. Other challenges include known cost and maintenance issuesassociated with linear motors.

SUMMARY

In some aspects, an active vibration control device configured tocontrol the position of a body includes at least one sensor configuredto provide input signals corresponding to movement of the body in atleast one direction, a rotary motor configured to control the positionof the body, and a linkage including at least two pivotably-joined linksconnecting the rotary motor to the body. The linkage is configured toconvert rotary motion output from the motor into a linear motion of thebody. The device further includes a controller which, based on the inputsignals from the at least one sensor, provides control signals to therotary motor which acts through the linkage to position the body in theat least one direction.

In another aspect of the invention, an actuator comprises a rotary motorincluding an output shaft and a motor housing; and a linkage connectedto the output shaft of the rotary motor. The linkage includes the motorhousing which has a housing pivot pin defining a first rotation axis anda first link fixed to the output shaft. The output shaft defines asecond rotation axis, and the second rotation axis is parallel to andspaced apart from the first rotation axis. The first link includes afirst link pivot pin disposed at a location spaced apart from the secondrotation axis and defines a third rotation axis that is parallel to thefirst rotation axis. The linkage includes a second link pivotablyconnected at a first end to the first link pivot pin. The second linkincludes a second link pivot pin defining a fourth rotation axis that isparallel to the first rotation axis. The second link pivot pin isdisposed between the first end of the second link and a predeterminedpoint of the second link. The linkage further includes a third linkpivotably connected at a first end to the housing pivot pin andpivotably connected at a second end to the second link pivot pin. Duringoperation of the actuator, rotation of the output shaft results in alinear motion of the predetermined point relative to the housing.

The active vibration control device and actuator may include one or moreof the following features: The torque generated by the motor at the bodyis substantially constant over a 100 degree angular rotation of theoutput shaft. The linkage is configured to convert the rotary motion ofthe output shaft to linear motion such that the motion of the body issubstantially proportional to the angular displacement of the outputshaft over a 180 degree rotation of the output shaft. The linkage isconfigured to convert the rotary motion of the output shaft to linearmotion such that the torque is substantially constant over a range ofdisplacement of the body of at least four inches.

The controller of the active vibration control device provides outputsignals to the rotary motor which acts through the linkage to positionthe body such that an attitude of the body controlled. The activevibration control device includes a second linkage, with one of saidlinkages connected to the output shaft of the motor on each of opposedsides of the motor. The device further includes a second rotary motorand a second linkage configured to control the position of the body, thefirst and second rotary motors arranged such that their respective rotoraxis are parallel. The device further includes a second rotary motor anda second linkage configured to control the position of the body, thefirst and second rotary motors arranged such that their respective rotoraxis are co-linear.

In certain implementations, the body includes a vehicle seat, forexample disposed in a vehicle, with the rotary motor, fixed relative toa floor of the vehicle, being disposed between the floor and the seat.The linear travel of the body is at least 4 inches. The controllerprovides control signals to the rotary motor to position the bodyaccording to a motion that is opposed and opposite to the motiondetected by the at least one sensor.

The actuator may further include one or more of the following features:The actuator includes a second linkage, and one of the linkages isconnected to the output shaft of the motor on each of opposed sides ofthe motor. Each of the housing pivot pin and the first and second linkpivot pins are supported on bearings, and the links are configured suchthat the bearings are substantially co-planar.

The active vibration control device and the actuator advantageouslyemploy a rotary motor and include a mechanism to converts rotary motionof the motor to linear motion. The actuator has many applications, oneof which is to control the position of an object along a linear path.The actuator, in which the rotary motor acts through a mechanicallinkage to position the object, has several advantages over knownpositioning devices which employ linear motors. For example, rotarymotors are much less expensive to fabricate and are more easily sealedthan a linear motor. In addition, rotary motors, in combination with themechanical linkage, are more compactly sized than a linear motor whileproviding equal or greater range of linear motion. This feature isimportant for example in vibration control of vehicle seats, where thespacing between the seat and floor, in which the control mechanism isdisposed, is limited.

Moreover, when combined with a controller, the actuator can be used as amotion control device. For example, in some implementations, theactuator combined with a controller can be used to provide activecontrol of valves in an internal combustion engine or a compressor. Insome implementations, the actuator combined with a controller can beconfigured to act as a position source, a velocity source or a forcesource. In some implementations, the actuator combined with a controllercan be used in an active vibration isolation control device. Forexample, the actuator and a controller can be used to control theposition and/or the acceleration of a vehicle seat, as explained furtherbelow, or to control the position and/or acceleration of the sprung massof a vehicle (i.e. the passenger compartment or an automotive vehicle).

A still further advantage of the actuator is that at least some of themechanical linkage is incorporated into the motor housing and rotorshaft, providing a actuator that is still more compact, less complex andrequires fewer parts. Furthermore, the actuator is a direct drive devicein which the rotor is connected to the object to be positioned via asingle rigid link, and without any intervening gears, belts or otherdevices which introduce error and/or complexity into positioningcontrol.

In a further aspect of the invention, a mechanism for converting rotarymotion into linear motion comprises a plate including a plate pivot pindefining a first rotation axis, and a first link fixed to a shaft. Theshaft is rotatably supported on the plate and defines a second rotationaxis, the second rotation axis being parallel to and spaced apart fromthe first rotation axis. The first link includes a first link pivot pindisposed at a location spaced apart from the second rotation axis anddefines a third rotation axis that is parallel to the first rotationaxis. The mechanism includes a second link pivotably connected at afirst end to the first link pivot pin. The second link includes a secondlink pivot pin defining a fourth rotation axis that is parallel to thefirst rotation axis, and the second link pivot pin is disposed betweenthe first end of the second link and a predetermined point on the secondlink. The mechanism further includes a third link pivotably connected ata first end to the plate pivot pin and pivotably connected at a secondend to the second link pivot pin. In the mechanism, rotation of theshaft results in a linear motion of the predetermined point relative tothe plate.

The mechanism may include one or more of the following features: Thepredetermined point moves linearly for about a 180 degree rotation ofthe shaft. The mechanism includes a first bar length defined by thedistance between the first link pivot pin and the shaft, a second barlength defined by the distance between the shaft and the plate pivotpin, a third bar length defined by the distance between the plate pivotpin and the second link pivot pin, and a fourth bar length defined bythe distance between the first link pivot pin and the predeterminedpoint, and the ratio of the first bar length to the second bar length tothe third bar length to the fourth bar length is 1:2:2.5:5. Each of theplate pivot pin, first and second link pivot pins and the shaft aresupported on bearings, and the bars are configured such that thebearings are substantially co-planar. The plate further comprises a stopmember configured to limit rotation of the first link relative to theplate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an actuator for converting rotary motionto linear motion.

FIG. 2 is a side sectional view of the actuator as seen along sectionline 2-2 of FIG. 1.

FIG. 3 is a schematic representation of a Hoeken's linkage.

FIG. 4 is a perspective view of the actuator of FIG. 1 illustrating thefour bars of the linkage.

FIG. 5 is a graph of rotor shaft angular displacement (degrees) versusdisplacement (inches) of a predetermined point of the first link.

FIG. 6 is an end view of the actuator of FIG. 1.

FIG. 7. is a graph of rotor shaft angular displacement (degrees) versustorque (Nm) output of the motor required to provide a constant 1100 Nforce at the predetermined point of the first link.

FIG. 8 is a graph of displacement (inches) of the second end of thefirst link versus torque (Nm) output of the motor required to provide aconstant 1100 N force at the predetermined point of the first link.

FIG. 9 is a perspective view of a position control device employing twoactuators shown in a retracted configuration.

FIG. 10 is a perspective view of the position control device of FIG. 9shown in an extended configuration.

FIG. 11 is a perspective view of an alternative implementation of aposition control device employing two actuators.

FIG. 12 is a perspective view of another alternative implementation of aposition control device employing two single-linkage actuators.

FIG. 13 is a schematic view of an active vibration control system for avehicle seat.

FIG. 14 is a sectional view of a portion of a cylinder bank of aninternal combustion engine in which the actuator of FIG. 1 is directlyconnected to an engine valve.

FIG. 15 is a sectional view of a portion of a cylinder bank of aninternal combustion engine in which the actuator of FIG. 1 is indirectlyconnected to an engine valve.

FIG. 16 is a perspective view of an alternative implementation of anactuator.

DETAILED DESCRIPTION

As will be described in greater detail below, an actuator including arotary driver combined with a linkage having particular mechanicalcharacteristics provides conversion of rotary to linear motion in amanner that is well suited for applications in which the linear range oftravel is maximized within a limited space.

FIGS. 1, 2, 4 and 6 show an actuator having this desired characteristicin the form of a rotary motor and a four-bar linkage. An alternativeimplementation of the actuator is shown in FIG. 16. FIGS. 5, 7 and 8illustrate the mechanical characteristics of the actuator includingproportionality of the displacement of a predetermined point on thelinkage to the angular displacement of the rotary motor, and a constantforce at the predetermined point for both angular displacement as wellas displacement of the predetermined point in the linear portion of themotion of the linkage 52 for a constant torque output of the rotarymotor. Several implementations of such an actuator when used as apositioning device are shown in FIGS. 9-12. In particular, the actuatorsare connected to and control movement of a platform. An implementationof the actuator used in an active vibration control system is describedwith reference to FIG. 13. In addition, an implementation of theactuator used to control engine valves is described with reference toFIGS. 14 and 15.

Referring now to FIGS. 1 and 2, the actuator 50 for converting rotarymotion to linear motion includes a rotary motor 60 supported by anddisposed within a motor housing 62. The actuator includes a firstlinkage 52 connected to, and driven by, one end of the motor 60. Thelinkage 52 is arranged as a Hoeken's linkage, and can be used toposition an object connected to the linkage along a linear path. Theactuator 50 advantageously provides a compact approach to linearlypositioning the object in space.

Although object positioning can be achieved using a single linkage 52,in the illustrated implementation, the actuator 50 further includes asecond linkage 252 connected to, and driven by, a second end of themotor 60. The second linkage 252 is a minor image of the first linkage52, and is configured to move synchronously and in concert with thefirst linkage 52, as discussed further below. Elements common to bothlinkages 52, 252 are identified by the same reference number. Thus, theconfiguration of each linkage will be described with reference to firstlinkage 52 only.

The rotary motor 60 includes a stator 72 fixed to the housing 62, and arotor 80 disposed coaxially within the stator 72 so as to be rotatableabout a rotor axis 82. The rotor 80 is a hollow cylindrical body havingopposed first and second ends 84, 85 rotatably supported on the housing62. The rotary motor 60 may be a conventional frameless kit motor suchas model K127300 made by Bayside® Motion Group, of Port Washington, N.Y.

The housing 62 includes closed sidewalls 63 capped at each end byhousing end plates 64. Each end plate 64 includes a plate pivot pin 68that extends outward in a direction parallel to the rotor axis 82,supports a bearing 194, and defines a first rotational axis 76 of thelinkage 52. In the illustrated implementation, the plate pivot pin 68,and thus the first rotational axis 76, overlies and is substantiallyvertically aligned with the rotor axis 82.

An end cap 100 is fixed to a first end 84 of the rotor 80. The end cap100 is a hollow cylindrical body having a closed first end 101. The endcap 100 is rotatably supported in an opening 66 formed in an end plate64 of the housing 60 so that the outer surface 102 lies generally withinthe plane of the end plate 64. Adjacent to the first end 101, an outerperiphery of the end cap 100 is supported by a rotor bearing 89 mountedin the housing end plate 64. The rotor bearing 89 may be a thin sectionbearing such as a Silverthin™ model SB035 angular contact bearing soldby Mechatronics Corporation of Preston, Wash.

The end cap 100 extends inward from the outer surface 102, andterminates at an open second end 103. The outer diameter of the end cap100 is reduced at the second end 103, forming an annular protrusion 128sized to be press fit within an inner surface of the rotor 80. Relativerotation of the end cap 100 with respect to the rotor 80 is prevented bysecuring the end cap 100 to the rotor. This can be achieved, forexample, by providing screws (not shown) in mutually aligned screw holes86, 130 formed in the rotor 80 and annular protrusion 128, respectively.Thus, the end cap 100 rotates with the rotor 80 and serves as an outputshaft of the motor 60. The rotational center 132 of the end cap 100 iscoaxial with the rotor axis 82, which corresponds to a second rotationalaxis of the linkage 52.

The outer surface 102 of the end cap 100 includes a protruding stepportion 104 formed at the periphery of the end cap 100 in the shape of asegment of a circle, in which the chord defining a side of the segmentis not a diameter of the end cap 100. A shoulder 106 is formed whichjoins the step portion 104 to the remainder of the outer surface 102. Anend cap pin 108 is provided in the step portion 104 adjacent to theperiphery of the end cap 100. The end cap pin 108 protrudes outwardlyfrom the step portion 104, supports a bearing 158, and defines a thirdrotational axis 110 of the linkage 52 that extends in parallel to therotor axis 82.

The motor 60 includes an external optical encoder 120 to determine theangular position of the rotor 80. In this implementation, an encodershaft 118 protrudes from an outer surface 102 of the first end 101coaxially with the rotor axis 82. The encoder shaft 118 is connected tothe input shaft 122 of the encoder using a flexible coupling 124,permitting accurate determination of the angular position of the rotor80. However, the actuator 50 is not limited to this configuration. Forexample, the motor 60 may be provided with an internal encoder.

A second end cap 200 is fixed to a second end 85 of the rotor 80. Thesecond end cap 200 is substantially similar in form and function to thatof the first end cap 100, and like elements of the second end cap 200are identified with the same reference numbers. For this reason, adetailed description of the second end cap 200 will be omitted except topoint out the following differences relative to the first end cap 100:The end cap 200 does not include an encoder shaft 118. The end cap 200is provided with a through hole 202 that is coaxially aligned with therotor axis 82. The through hole 202 provides access to the interior ofrotary motor 60, which is advantageous during assembly and disassemblyof the actuator 50.

As stated above, the linkage 52 is arranged as a Hoeken's linkage. AHoeken's linkage is a four-bar linkage that converts rotational motionto approximate straight line motion. With reference to FIG. 3, theHoeken's linkage includes a rotating first bar I, a fixed second bar IIwhich joins the first bar Ito a fourth bar IV, a third bar III driven atone end by the first bar I, and the fourth bar IV which supports a midportion of the third bar III. Due to the rotation of the first bar I,the point P of the third bar III moves along the closed-loop path 53indicated by the dashed line. As seen in the figure, the path includes asubstantially linear portion 55.

Referring to FIG. 4, the four bars of the linkage 52 are defined asfollows:

The first bar 116 of the linkage 52 is provided by the end cap 200. Morespecifically, the first bar 116 includes the portion of the end cap 200extending between the rotational center 132 of the end cap 200 and theend cap pin 108. The first bar 116 rotates relative to the housing 62about the second rotational axis 82 in a plane corresponding to outersurface 102 of the end cap 200.

The second bar 88 of the linkage 52 is provided by the housing 62. Morespecifically, the second bar 88 includes a portion of the end plate 64and extends between the plate pivot pin 68 and the rotational center 132of the end cap 200. The second bar 88 is a fixed bar relative to thehousing 62, and defines the orientation of the linear motion produced bythe linkage 52.

The third bar 151 of the linkage 52 is provided by the first link 150.The first link 150 is an elongate rigid bar of rectangular crosssection, and includes a first end 152, and a second end 154 opposed tothe first end 152. The first and second ends 152, 154, and the mid point156 between the first and second ends 152, 154 are provided with throughholes 165 that extend between opposed broad faces 166, 168 of the firstlink 150. The bearings 158, 160, (midpoint bearing not shown) are pressfit into the respective through holes 165 and are sized and shaped toreceive a pivot pin. For example, the bearing 158 at the first end 152of the first link 150 receives the end cap pin 108, and permits rotationof the first link 150 about the end cap pin 108 (and third rotationalaxis 110) relative to the housing 62 and the end plate 100. The bearingdisposed at the mid point 156 supports a link pin 162. The link pin 162protrudes outwardly from both broad faces 166, 168 of the first link150, and defines a fourth rotational axis 164 of the linkage 52 thatextends in parallel to the rotor axis 82. Constituted by the first link150, the third bar 151 of the linkage 52 extends between the end cappivot pin 108 and the centerline of the bearing 160 (which coincideswith point P in FIG. 4).

The fourth bar 181 of the linkage 52 is provided by the second link 180.The second link 180 is an elongate rigid bar of rectangular crosssection, and includes a first end 182, and a second end 184 opposed tothe first end 182. The first end 182 is provided with a through hole 195that extends between opposed broad faces 196, 198 of the second link180. A bearing 194 is press fit into the through hole 195 and is sizedand shaped to receive the plate pin 68. Thus, the first end 182 of thesecond link 180 rotates about the plate pin 68 (and first rotationalaxis 76) relative to the housing 62. The second end 184 of the secondlink 180 is bifurcated so that the distance between the broad faces 196,198 at the second end 184 is greater that that at the first end 182, andso that the second end 184 forms a yoke including spaced yoke arms 186,188 which straddle mid portion of the first link 150 and engage the linkpin 162. Thus, the second end 184 of the second link 180 rotates aboutthe link pin 162 (and the fourth rotational axis) relative to thehousing 62 and the first link 150. Constituted by the second link 180,the fourth bar 181 of the linkage 52 extends between the plate pivot pin68 and the link pin 162.

By providing the second link 180 with yoke arms 186, 188, the first end182 of the second link 180 can be arranged to be in the same plane asthe first link 150. In addition, by providing the end cap 100 with thestep portion 104, and by locating the end cap pin 108 on the stepportion 104, a space is provided between the main link 150 and thehousing 64 which can accommodate the inner yoke arm 188. In combination,these features advantageously permit the pivot pin bearings 158, 160 and194, which are conventional radial ball bearings, to be arranged withina single plane, whereby twisting loads on the links are avoided when inuse. However, the linkage 52 is not limited to this configuration, andin some embodiments, the second link 180 may be formed without a yokeand may instead be formed having an offset portion or having a linearconfiguration.

The linkage 52 is used to convert the rotary motion of the rotor 80 intoa linear motion at a predetermined point P on the first link 150. In theillustrated implementation, the center of the bearing 160 at the secondend 154 of the first link 150 is defined as the predetermined point P atwhich linear motion is generated. By adjusting the relative lengths ofthe respective first through fourth bars 116, 88, 150, 180, the motionof the point P can be specified. In the actuator 50, the first barlength is defined by the distance between the end cap pin 108 and therotational center 132 of the end cap 200, the second bar length isdefined by the distance between the rotational center 132 of the end cap200 and the plate pin 68, the third bar length is defined by thedistance between the end cap pin 108 and the point P, and the fourth barlength is defined by the distance between the link pin 162 and the platepin 68. In the illustrated implementation, the bar lengths are asfollows: The first bar 116 is 1 inch, the second bar 88 is 2 inches, thethird bar 151 is 5 inches and the fourth bar 181 is 2.5 inches. Therange of linear travel which is achieved with this configuration isabout 4 inches. Of course, an increased range of linear travel can beobtained by proportionally increasing the size of the bars of thelinkage. For example, for respective first through fourth bar lengths of1.25 inches, 2.5 inches, 6.25 inches and 3.125 inches, the range oflinear travel which is achieved is about 5 inches. Conversely, forapplications in which a smaller range of linear travel is required, themechanism can be scaled down, resulting in an even more compact device.

In the linkage 52, the ratio of the first bar length to the second barlength to the third bar length to the fourth bar length is 1:2:5:2.5. Byusing these proportions, at least the following several advantages arerealized:

The linear portion of the motion of the point P occurs along a line thatis parallel to the fixed second bar 88. In the illustratedimplementation, the fixed second bar 88 is oriented vertically, and thusthe linear portion of the motion of the point P also has a verticalmotion.

Furthermore, as shown in FIG. 5, the motion of the point P issubstantially proportional to the angular displacement of the end cappin 108 over a 180 degree rotation of the rotor 80. That is, the point Pmoves approximately linearly within the range of rotational motion ofthe rotor 80 indicated by reference lines A and B, corresponding to anapproximate range of 180 degrees.

In the actuator 50, two external links 150, 180 are provided whichrespectively serve as the third III and fourth IV bars of the Hoeken'sfour-bar linkage. The remaining two bars (the first and second bars I,II) are provided by the components of the motor 60 and motor housing 62.Specifically, the second end cap 200 which incorporates the first bar116 serves as the rotating first bar I of the Hoeken's linkage, and themotor housing 64 which incorporates the second bar 88 serves as thefixed second bar II of the Hoeken's linkage. This configuration, inwhich the first and second bars 116, 88 are not formed as external linksbut instead are incorporated into the motor assembly itself, reduces thenumber of components required to achieve the desired motion, and resultsin a compact actuator assembly.

Referring now to FIG. 6, the actuator 50 is configured so that thesecond end 154 of the first link 150 is constrained to move back andforth within the linear motion range identified between A and B of FIG.5. In some implementations, a controller 14 (FIG. 13) connected to themotor 60 prevents the rotor 80, and thus the end cap 100, from rotatingbeyond the 180 degree range. In addition, a stop member 90 is providedto mechanically interfere with the shoulder 106 of the outer surface102, whereby rotation beyond the linear range is prevented. The stopmember 90 is fixed to the housing 62, and extends radially inward tooverlie a portion the opening 66 in the end plate 64. When the linkageis in a fully extended configuration corresponding to one end of thelinear range (shown in solid lines in FIG. 4), a first portion theshoulder 106 abuts a first stop surface 96 of the stop member 90. Inthis position, the first end 152 of the first link 150 is positioned ona horizontal line passing through the rotor axis 82 at a location to theleft of the rotor axis 82 as viewed in the figure. In addition, asviewed in the figure, the point P is located at a position that islateral to, and above an upper side of, the housing 62. When the end cap100 rotates counterclockwise, the linkage 52 moves downward, and thepoint P travels downward along a linear path L. When the linkage 52 isin a retracted position corresponding to the opposed end of the linearrange (shown in dashed lines in FIG. 4), a second portion of theshoulder 106 abuts a second stop surface 98 of the stop member 90. Inthis position, the first end of the first link 150 has rotated through a180 degree arc, and is now positioned on the horizontal line passingthrough the rotor axis at a location to the right of the rotor axis 82as viewed in the figure. In addition, the point P is now located at aposition that is lateral to, and below an upper side of, the housing 62.

Further advantageously, in one embodiment as shown in FIG. 7, thefour-bar linkage 52 is configured to convert the rotary motion of therotor 80 to linear motion such that the torque output of the motor 60required to provide a constant 1100N force at the point P issubstantially constant over most of the angular displacement range ofthe motor associated with the linear travel range of the point P. Thetorque output of the motor 60 is substantially constant within the rangeof rotational motion of the rotor 80 indicated by reference lines C andD, corresponding to a range of about 100 degrees.

In addition, in one embodiment as shown in FIG. 8, the four-bar linkage52 is configured to convert the rotary motion of the rotor 80 to linearmotion such that the torque output of the motor 60 required to provide aconstant 1100N force at the point P is substantially constant over mostof the linear range of motion of point P. The torque output of the motor60 is substantially constant over the majority of the range of tiplinear displacement indicated by reference lined E and F, correspondingto about 4 inches.

Referring to FIGS. 9 and 10, the position control device 350 is animplementation of the actuator 50, in which the device 350 includes twoactuators 50, 50′ arranged such that the rotor axes 82, 82′ of therespective rotary motors 60, 60′ are substantially coaxial. In addition,the linkages 52, 252 of the first actuator 50 are configured to rotatein opposition to the linkages 52′, 252′ of the second actuator 50′. Inthe illustrated implementation, the position control device 350 is usedto control the vertical position of a platform 16 relative to a base 22,and is connected to the platform 16 through several downwardly extendinglegs 18. In particular, each leg 18 includes a pivot pin 20 which isrotatably supported by the bearing 160 at the second end 154 of therespective first link 150 of each linkage 52, 52′, 250, 250′, a locationcorresponding to point P. In FIG. 9, the position control device 350 isshown in a first, retracted configuration in which the vertical distancebetween the platform 16 and the base 22 is a distance d1. In thisimplementation, there is substantially no vertical spacing between theplatform 16 and the housings 62, 62′, whereby the retractedconfiguration is very compact. In addition, the platform 16 issubstantially centered over the position control device 350. In FIG. 10,the position control device 350 is shown in a second, extendedconfiguration in which the vertical distance between the platform 16 andthe base 22 is a distance d2, where d2 is greater than d1. The platform16 remains centered over the position control device 350 during thetransition between retracted and extended configurations, and while inthe extended configuration. Although the illustrated implementationshows the actuators 50, 50′ as being axially spaced a distance s1, thisconfiguration is non-limiting. For example, the two actuators 50, 50′may be spaced apart a distance which is greater or less than s1.

Referring to FIG. 11, position control device 450 is an alternativeimplementation of the actuator 50 Like the previous position controldevice 350, the position control device 450 includes two actuators 50,50′, the second actuator 50′ being identical to the first actuator 50.In the position control device 450, the actuators 50, 50′ are arrangedsuch that the rotor axes 82, 82′ of the respective rotary motors 60, 60′are parallel and spaced apart. In addition, the linkages 52, 252 of thefirst actuator 50 are configured to rotate in opposition to the linkages52′, 252′ of the second actuator 50′. In the illustrated implementation,the position control device 450 is used to control the vertical positionof a platform 16 relative to a base 22, and is connected to the platform16 through several legs 18. In particular, each leg 18 includes a pivotpin 20 which is rotatably supported by the bearing 160 at the second end154 of the respective first link 150 of each linkage 52, 52′, 250, 250′,a location corresponding to point P. Although the illustratedimplementation shows the axes 82, 82′ of the actuators 50, 50′ as beingspaced a distance s2, this configuration is non-limiting. For example,the axes 82, 82′ may be spaced apart a distance which is greater thans2. In addition, although the illustrated implementation shows theactuators 50, 50′ as being co-planar, the actuators can instead beoffset to lie in different planes while maintaining parallel axes 82,82′.

Referring to FIG. 12, position control device 550 is another alternativeimplementation of the actuator 50. The position control device 550includes two single-linkage actuators 250, 250′. In particular, eachactuator 250, 250′ is provided with a single linkage 52, 52′. In theposition control device 550, the actuators 250, 250′ are arranged suchthat the rotor axes 82, 82′ of the respective rotary motors 60, 60′ arecoaxial. In addition, the linkage 52 of the first actuator 250 isconfigured to rotate in opposition to the linkage 52′ of the secondactuator 250′. In the illustrated implementation, the position controldevice 550 is used to control the vertical position a platform 16relative to a base 22, and is connected to the platform 16 throughseveral legs 18. In particular, each leg 18 includes a pivot pin 20which is rotatably supported by the bearing 160 at the second end 154 ofthe respective first link 150 of each linkage 52, 52′, a locationcorresponding to point P. The position control device 550 operatessimilarly to the position control device 350, but is less complex,requires fewer bearings, and is more compact in the axial direction thanthe position control device 350. Although the illustrated implementationshows the two actuators 250, 250′ as being axially abutting, thisconfiguration is non-limiting, whereby the actuators 250, 250′ may beaxially spaced apart.

In each of the above-described position control devices 350, 450, 550,by using linkage mechanisms arranged on opposing sides, when theactuators 50 move in unison, the respective reaction torques at the base22 due to the load significantly reduced. In addition, by using tworotary motors 60, 60′ to position platform 16 rather than a singlerotary motor 60, each of the two rotary motors 60, 60′ can be reduced insize, resulting in a mechanism that is even more compact. In addition,in some implementations the respective linkages 52, 252, 52′, 252′ canbe mechanically tied together so that the platform 16 can remain levelin the event of failure of one of the rotary motors 60, 60′.

Referring to FIG. 13, the position control device 350 may be used in anactive vibration control system 5 used in a vehicle 2 to mitigate oreliminate vehicle seat 8 vibration resulting from vibration of thevehicle frame 4. The vehicle seat 8 is fixed to a rigid seat base 10,and supports at least one sensor 12. For example, the sensor 12 mayinclude an accelerometer for detecting motion of the seat relative tothe ground g. The seat 8 and base 10 rest on and are supported above thevehicle frame 4 by the position control device 350. The position controldevice 350 may be attached indirectly to the vehicle frame via ancillaryseat support structures, or attached directly to the frame itself,whereby the position control device 350 is fixed relative to the vehicleframe 4. The position control device 350 serves to position the base 10,and thus the seat 8, relative to the vehicle frame 4 based on controlsignals received from a controller 14. The controller 14 receivessignals including seat movement data from the sensor 12, and encodersignals indicating rotor position relative to the housing 62, 62′. Basedon these signals, the controller 14 outputs control signals to therotary motors 60, 60′ of the position control device 350 such that theposition of the vehicle seat 8 is controlled relative to the vehicleframe. Although the illustrated implementation employs the positioncontrol device 350, this is non-limiting. For example, any of thedisclosed position control devices 450, 550 may be substituted fordevice 350. Moreover, a single actuator 50, 250 may be used incombination with supplementary seat support structure to form an activevibration control system.

In some implementations, the respective rotary motors 60, 60′ arecontrolled to position the base 10, and thus the seat 8, so as to cancelthe detected seat motions in order to isolate the seat 8 from vehiclevibration. In some implementations, the respective rotary motors 60, 60′are controlled to act in concert. For example, the distance of thesecond end 154 of the first link 150 of both actuators 50, 50′ from thevehicle frame 4 is controlled to be the same. In other implementations,the rotary motor 60 of the first actuator 50 may be controlledindependently of the rotary motor 60′ of the second actuator 50′,whereby the attitude of the seat base 10 relative to the vehicle frame 4may be controlled. In such an implementation, at least one additionaldegree of freedom would be required between the linkages 52, 252, 52′,252′ and the seat base 10 to permit relative motion between thesecomponents. This can be accomplished, for example, by providing anadditional pivot point at a location G.

The active vibration control system 5, which employs the actuators 50 toconvert rotary motion output from the rotary motor 60, 60′ into a linearmotion, has several advantages relative to a control system employing alinear motor. For example, rotary motors are much less expensive tofabricate and are more easily sealed than a linear motor. In addition,rotary motors, in combination with the mechanical linkage, are morecompactly sized than a linear motor while providing equal or greaterrange of linear motion. This feature is important for example invibration control of vehicle seats, where the spacing between the seatand floor, in which the control mechanism is disposed, is limited. Astill further advantage of the actuator is that at least some of themechanical linkage is incorporated into the motor housing and rotorshaft, thereby providing a actuator that is even more compact, lesscomplex and requires fewer parts.

Furthermore, in some implementations, the actuator 50 can be a directdrive device in which the rotor is connected to the object to bepositioned via a single rigid link, and without any intervening gears,belts or other devices which introduce error and/or complexity intopositioning control.

In addition, a further advantage to using the position control device350 in the active vibration control device 5 lies in the fact thatrotary motors are inherently more efficient than linear motors. Forexample, there are 3 different armature/stator relationships which canbe useful in a linear motor: 1) An under hung relationship in which thecoils and poles of the stator extend beyond the length of the armaturemagnets, so that as the magnets move back and forth, the armature for atleast some range of travel remains within the stator poles. The designmay be such that at maximum excursion the armature still stays withinthe coils, or it may begin to extend past them at some point. 2) An evenhung relationship in which the armature magnets are the same length asthe stator poles. In this design, as soon as the armature begins tomove, some magnets move outside of the stator poles. 3) An over hungrelationship in which the armature magnets exceed the length of thestator poles. In the over hung design, movement of the armature does notchange the amount of magnet residing within the stator poles, over atleast some excursion range. In this design, the whole excursion rangecan be used, or just some part.

In any of the above described relationships, a trade off is made betweenefficiency and cost. For example, as soon as some magnets move outsideof the stator poles, their contribution to force output is reducedrapidly. Due to the relatively high expense of the magnets, is desirableto make full use of the magnets all the time.

When used in limited space conditions as found in the active seatvibration control application, and for example, when using an under hungdesign, it is possible to make full use of the magnets. However, theamount of force produced over the majority of the excursion range for afixed input current will be less than if more magnets were used. Thus,the efficiency of the linear motor is reduced, where efficiency isdefined as output mechanical power divided by input electrical power. Aneven hung design trades off between these factors.

The advantage in using a rotary motor rather than a linear motor is thatit is inherent in the rotary design that all the magnets see the polesof the stator for all angles of rotation. This is an optimum conditionfor trading off efficiency and cost. For this reason it is advantageousto use a rotary motor and a mechanism for converting rotary motion tolinear motion, rather than a linear actuator, for linear positioningapplications.

Although the illustrated implementation shows the actuator 50 forconverting rotary motion to linear motion used to actively controlvibration of a vehicle seat, the actuator 50 is not limited to thisapplication. For example, the actuator 50 is also suitable for use inother aspects of vehicle vibration control including wheel suspensionsystems and engine vibration control systems. Moreover, the actuator 50is not limited to vibration control, and has general application toobject position control. For example, the actuator can be used tocontrol engine valve motion, whereby engine efficiency can be improved.

Referring now to FIG. 14, the actuator 50 may be used in an internalcombustion engine 700 to control engine valve position, replacingtraditional cam-shaft driven valve trains. The engine 700 has aplurality of cylinders 712 (only one cylinder is shown) disposed in acylinder block 718 arranged in a V configuration to form cylinder banks714 with the upper ends of the cylinders 712 being closed by cylinderheads 716. A pair of inlet valves 740 (only one of which is shown) arelongitudinally aligned on the inner side of the cylinder 712 and itsassociated combustion chamber 744, and an exhaust valve 762 is locatedon the outer side of the cylinder 712. An igniter in the form of a sparkplug 766 or similar device is also disposed in the combustion chamber744 of each cylinder 712.

An actuator 50 is provided for each inlet and exhaust valve 740, 762,and predetermined point P of the first link 150 is pivotably connectedto the corresponding valve stem. The actuator 50 serves to position theinlet and exhaust valve 740, 762 relative to the cylinder block 718based on control signals received from a controller (not shown). Thecontroller receives signals including valve movement data from encodersignals indicating rotor position relative to the housing 62, andcrankshaft position data. Based on these signals, the controller outputscontrol signals to the rotary motor 60 of the actuator 50 such that theposition of the valve 740, 762 is controlled relative to the cylinderblock 718.

Referring to FIG. 15, in other implementations, the actuator 50 may beindirectly connected to the respective inlet and exhaust valves 740,762. For example, the predetermined point P of the first link 150 can beconnected to an inlet push rod 730. The push rod 730 actuates an inletrocker arm 732 that rocks on a pivot axis 734. Rocker arm 732 includes apair of actuating arms 736 each of which preferably carries a hydrauliclash adjuster 738. The lash adjusters 738 engage the pair of inletvalves 740. Although hidden in this view by the actuator 50 and theinlet push rod 730, another actuator 50 is connected to an exhaust pushrod for actuating a primary rocker arm 754 which is pivotable on thesame pivot axis 734 as the inlet rocker arm 732. The primary rocker arm754 in turn engages a secondary push rod 756 which engages with asecondary rocker arm 758. An actuating arm of rocker arm 758 directlyengages the exhaust valve 762. Like the previous implementation, theactuator 50 serves to position the inlet and exhaust valve 740, 762relative to the cylinder block 718 based on control signals receivedfrom a controller (not shown). The controller receives signals includingvalve movement data from encoder signals indicating rotor positionrelative to the housing 62, and crankshaft position data. Based on thesesignals, the controller outputs control signals to the rotary motor 60of the actuator 50 such that the position of the valve 740, 762 iscontrolled relative to the cylinder block 718.

Although the engine valve position control implementations illustratedhere provide an actuator 50 for each engine valve 740, 762 of thecylinder 712, this is non-limiting. For example, a single actuator 50could be used to control multiple valves. For example, a single actuatorcould simultaneously actuate multiple input valves coupled to a singlecombustion chamber.

Using the actuator 50 to control valve operation advantageously allowsmotion of the valves to be decoupled from rotation of the enginecrankshaft. In addition, a fully controllable valve allows completecontrol of timing and lift, over the entire range of engine speeds. Thisallows valve operation to be optimized over all operating conditions. Italso allows variation with operation, enabling operation in an engineefficiency mode, or in maximum power delivery mode. It makes enginecylinder de-activation easy, and allows more complex de-activationschemes. For example, rather than de-activating an entire cylinder bankas is current practice, a portion of a cylinder bank or an individualcylinder can be deactivated. In addition, use of actuator 50 to controlvalve operation allows allow an engine to be self started, without theneed for a separate starter to rotate the crankshaft.

Using the engine valve control system described herein, including theactuator 50 provides conversion of rotary to linear motion in a mannerthat is well suited for this application in which the linear range oftravel is maximized within a limited space. For example, unlike a linearactuator which must be arranged in line with the valve shaft and extendupwards from the valve stem, the actuator 50 can control a valve liftprofile at will from a location to one side of the valve, and thus doesnot add height to the valve train. Location of the actuator 50 to theside of the valve can provide linear displacement of the valve withoutrequiring a lever or rocker arm, which can significantly reduce frictionlosses and wear of the valve guides.

This feature, in combination with the compact size of the actuator 50,permits packaging of the actuators so that when multiple valves percylinder are employed, multiple actuators can be fit around the cylinderor positioned remotely about the periphery of the cylinder while stillproviding full control of each valve.

Because the actuator 50 employs a rotary motor 60 which acts through alinkage to control valve position, the actuator 50 can be located awayfrom the cylinder head 716. This is advantageous since this permits theactuator 50 and sensors to avoid high temperatures associated withcylinder exhaust valves and manifold. This increases the amount of powerthan can be dissipated in the coils of the actuator before thermaldemagnetizaton temperatures are reached. In addition, since the actuatormotors are located away from the valves themselves, design of coolingdevices is simplified. For example, cooling jackets can be provided thatsurround all the actuator motors without interfering with otherstructures.

In the actuator 50, a rotary encoder 120 is used to sense position. Thissensor is located with the rotary motor 60, away from the location ofthe valve. The rotary encoder 120 can be much less expensive and morereliable than linear position and velocity sensors. It also can belocated in a position where it sees lower temperatures. Because theactuator 50 employs a rotary motor 60, design and manufacture ofreliable sensors to detect valve position and velocity is relativelystraightforward.

Because the actuator 50 employs a rotary motor 60, this device is wellsuited for use in the engine 700 since substantial peak power at highengine speeds is required to overcome cylinder cracking pressure andopen the exhaust valves. This requirement puts extreme demands on thepower electronics of the system, and also drives a need for maximumefficiency in the actuator. For the reasons discussed above, a rotarymotor is inherently more efficient than, for example, an actuatoremploying linear motor. The relative efficiency of the rotary motor canbe used to possibly downsize the motor itself, or to reduce theelectrical power requirements, or both.

From a packaging perspective, the actuator 50 including the rotary motor60 and linkage 52 has much lower profile than a linear motor, and due tothe linkage connection between the motor and the valve, the actuator canbe integrated with the valve train such that the rotary motors does notsit directly over the valves. For example, the actuator 50 can bedisposed between cylinder banks of V engines. Moreover, a separatelinkage (if necessary) can connect the point P of the linkage 52 to thevalves. By locating the rotary motor of the actuator away from thevalves, it becomes much easier to package an actively controlledmultiple valve per cylinder system.

Precise control is needed to avoid having the valve collide with thevalve seat. The particular relationship between torque and positionobtained by the actuator 50 simplifies the control of the engine valve.

Referring to FIG. 16, actuator 650 is an alternative implementation ofthe actuator 50. The actuator 650 is substantially similar to theactuator 50, except that the end caps 100, 200 of the actuator 50 aremodified to improve ease of assembly. In particular, the modified endcaps (not shown) are formed having a reduced outer diameter, and thelarge diameter rotor bearings 89 which support the end caps 100, 200 arereplaced with similar bearings of smaller diameter. Due to the reduceddiameter of the modified end caps, a third link 280 is provided whichcorresponds to the first bar 116 of the four-bar linkage and isdimensioned accordingly.

Although the illustrated implementation is described as using specificmotor and bearings, the present invention is not limited to thesecomponents and it is understood that the motor and bearings are selectedbased on the requirements of the specific application.

A selected illustrative embodiment of the mechanism for convertingrotary motion to linear motion is described above in some detail.However, it should be understood that only structures considerednecessary for clarifying the present invention have been describedherein. Other conventional structures, and those of ancillary andauxiliary components of the system, are assumed to be known andunderstood by those skilled in the art. Moreover, while a workingexample of the present invention has been described above, the presentinvention is not limited to the working example described above, butvarious design alterations may be carried out without departing from thepresent invention as set forth in the claims.

What is claimed is,:
 1. An active vibration control device configured tocontrol the position of a body, the device comprising: at least onesensor configured to provide input signals corresponding to movement ofthe body in at least one direction; a rotary actuator configured tocontrol the position of the body, and a linkage comprising apivotably-joined link connecting the rotary actuator to the body, thelinkage connected to and driven by the rotary actuator, the linkageconfigured to convert rotary motion output from the rotary actuator intoa linear motion of the body, a controller which, based on the inputsignals from the at least one sensor, provides control signals to therotary actuator which acts through the linkage to position the body inthe at least one direction.
 2. The active vibration control device ofclaim 1 wherein the torque required by the rotary actuator to provide aconstant force at the body is substantially constant over a 100 degreeangular rotation of an output shaft of the rotary actuator.
 3. Theactive vibration control device of claim 1 wherein the linkage isconfigured to convert the rotary motion of an output shaft of the rotaryactuator to linear motion such that the motion of the body issubstantially proportional to the angular displacement of the outputshaft over a 180 degree rotation of the output shaft.
 4. The activevibration control device of claim 1 wherein the linkage is configured toconvert the rotary motion of an output shaft of the rotary actuator intolinear motion such that the torque required by the rotary actuator toproduce a constant force at the body is substantially constant over arange of displacement of the body of at least four inches.
 5. The activevibration control device of claim 1 wherein the linkage is connected toan output shaft of the rotary actuator on one side of the rotaryactuator, and the device further comprises a second linkage connected tothe output shaft of the rotary actuator on a side of the rotary actuatoropposed to the one side.
 6. The active vibration control device of claim1 further comprising a second rotary rotary actuator and a secondlinkage configured to control the position of the body, the first andsecond rotary actuators arranged such that their respective rotor axesare parallel.
 7. The active vibration control device of claim 1 furthercomprising a second rotary actuator and a second linkage configured tocontrol the position of the body, the first and second rotary actuatorsarranged such that their respective rotor axes are co-linear.
 8. Theactive vibration control device of claim 1 wherein the body comprises avehicle seat.
 9. The active vibration control device of claim 8 furthercomprising a supplementary seat support structure.
 10. The activevibration control device of claim 9 wherein the rotary actuator isattached indirectly to a frame of the vehicle via the supplementarysupport structure, whereby the rotary actuator is fixed relative to thevehicle frame.
 11. The active vibration control device of claim 8wherein the seat is disposed in a vehicle, and the rotary actuator,fixed relative to a floor of the vehicle, is disposed between the floorand the seat.
 12. The active vibration control device of claim 1 whereinthe controller provides control signals to the rotary actuator tominimize the acceleration sensed by the at least one sensor.
 13. Theactive vibration control device of claim 1 wherein a rotor of the rotaryactuator is prevented from rotating beyond a predetermined range. 14.The active vibration control device of claim 13 wherein the controllerprevents the rotor from rotating beyond the predetermined range.
 15. Theactive vibration control device of claim 13 wherein a mechanical stopmember is provided to prevent the rotor from rotating beyond thepredetermined range.
 16. An active vibration control device configuredto control the position of a body, the device comprising: at least onesensor configured to provide input signals corresponding to movement ofthe body in at least one direction; a rotary actuator configured tocontrol the position of the body, and a linkage comprising apivotably-joined link connecting the rotary actuator to the body, thelinkage configured to convert rotary motion output from the rotaryactuator into a linear motion of the body, a controller which, based onthe input signals from the at least one sensor, provides control signalsto the rotary actuator which acts through the linkage to position thebody in the at least one direction, wherein; the body comprises avehicle seat, the seat is disposed in a vehicle, and the rotary actuatoris disposed between a floor in the vehicle and the seat.
 17. The activevibration control device of claim 16 further comprising a supplementaryseat support structure.
 18. The active vibration control device of claim17 wherein the rotary actuator is attached indirectly to a frame of thevehicle via the supplementary support structure, whereby the rotaryactuator is fixed relative to the vehicle frame.
 19. The activevibration control device of claim 16 wherein the linkage is connected toan output shaft of the rotary actuator on one side of the rotaryactuator, and the device further comprises a second linkage connected tothe output shaft of the rotary actuator on a side of the rotary actuatoropposed to the one side.
 20. The active vibration control device ofclaim 16 wherein a rotor of the rotary actuator is prevented fromrotating beyond a predetermined range.
 21. The active vibration controldevice of claim 16 wherein the controller prevents the rotor fromrotating beyond the predetermined range.
 22. The active vibrationcontrol device of claim 16 wherein a mechanical stop member is providedto prevent the rotor from rotating beyond the predetermined range.